regex

-E flag in grep

Match from start : ^
Match from ending: $

(a) : group parts of a regex, processed together
[a-z] : list of characters to search for
{1,10} : number or range, indicates how many times pattern must repeat
[^k] : excludes character from charset

\w: alphanumeric
\d: digit
\s: whitespace
Capital of above is opp, eg not alphanumeric, not digit and so on
. : any character (to capture . use . that way it escapes it

* : 0 or more
+ : 1 or more
? : 0 or 1

| : OR operator
.* : AND operator, order matters